Using an inverter as a UPS (automating power supply to a sump pump)

[politics123]

My example is for a sump pump, but really, this is about providing inexpensive back-up power to any small motors, fridges, etc.

My sump pump runs on 120v AC power. We don't lose power often (1-2x per year), but if that were to happen during a rainstorm, my basement would flood with water. In the future, I'll install either a generator or a whole-house UPS (with solar) and also a redundant sump pump, but those projects are expensive, and I'm thinking, in the short-term, I could get by with spending a lot less. I also found a few battery-backup sump pump systems ($500 or so without the battery), all of which require installing a second pump -- which are also expensive, and have questionable pump reliability.

Anyway, I have two options:
A) Connect invert to battery and whenever we lose power, manually turn on the inverter, manually unplug the sump pump from the wall, and manually plug it into the inverter. Then, when power is restored, I can plug the sump pump back into the wall.
B ) Using a 3-way lightswitch, perform all the electrical work, but still have to turn-on the inverter and flip the sump pump to run on its secondary power source.
C ) Automate!

Obviously, since I'm an active participant here, there's only one way to go. Note: I'd like to automate the power supply to the sump pump (but let the sump pump continue to run based on its float switch)

Here's the assets I have:
1) 1/4HP Sump Pump
2) Elk M1 Gold
3) Duracell (Xantrex) 1000 watt inverter (2000 watt surge). Cost me $45 from Amazon from amazon... couldn't refuse, since if this project fails the inverter will also come in handy while camping... you know, to power my portable M1 gold system... I set of strobes and an alarm if any racoons come close to my picnic basket! JK! (PS Not a half-bad idea, though)

Here's the assets I need to acquire:
1) 12v deep cycle battery (since cost is an issue, I'm thinking of either flooded or sealed, not AGM or GELL)
2) relays/switches
3) battery charger

Design Requirements:
1) This is for an existing 1/6HP (120v AC) sump pump, but I'm seriously thinking about upgrading this to a high-quality 1/3 HP
2) Sump should always run on normal household AC when there is AC power to its circuit.
3) Sump should run off of 12v DC battery + Inverter when there isn't AC power to the house. This doens't need to be an instant cut-over... within 60 seconds is fine.
4) When AC power is reestablished after an outtage, the power should revert back to household AC. This also doesn't have to be instant cut-over.
5) At no time should the sump be connected to both AC power and the inverter power (even momentarily).
6) Ideally, the inverter should be disconnected from the battery until power is lost and the inverter is needed. This will prevent unwanted discharge (300mA) when there is no load
7) Also, I'll be acquiring a battery charger. I could spend a bunch of money on a top-end charger that maintains a battery at peak charge, or I can buy a cheapo unit and automate it such that it charges the battery for 24 hrs every 2 weeks.


I attached a quick schematic of how I think this should be connected

Questions
1) Is there a problem connecting the inverter ground to household AC ground?
2) The ELK-912 and 924 relays might work --> they can be powered either from my ELK (with a rule) or from a wall-wart plugged into the same circuit as the sump pump is currently. They support 40amp in-rush and are rated for a 1/4 HP motor... which is what I have. However, if I wanted to upgrade my sump to 1/3 HP, I'd need a different set of relays. Anyone know of a good source for slightly higher amperage, but still inexpensive, relays? These need to be form c relays, right (break before contact)?
3) I can use the ELK-924 as a DPST switch, right? I just don't connect anything to the other pole?
4) Besides relays, does anyone know of a manu-matic switch that could be used. eg: is there a true 3-way automated (eg: zwave) light-switch that can be repurposed as a DPDT switch?


Estimate Project Costs:
Relays: 2-3 relays... around $30
Battery: $50-$100 (depending on reserve capacity and whether I do flooded, sealed, AGL, or GELL)
Charger: $50 or so for Battery Tender (able to leave connected), $15 for cheapo-charger (which I could regulate using an optional SPST switch)
Inverter: $45
Misc Romex cable and a spare power outlet: got plenty
Total between $150 and $250.

 

[deranged]

If you 120VAC 1/3 HP pump draws 5 Amps at 120VAC, the battery draw for the inverter is going to be about 50 Amps ( rough numbers ).

This is some serious amps for a battery and any store battery will not last that long.

I use a slightly simpler method that so far has worked very well. I added a secondary 12Volt DC pumps, that could easily run off the batteries.


A 12 Volt DC pump would draw a lot less current and be easier to wire and control. Since this is for Emergency purpose and I don't have to pump that far I use 2 1500 GPH 12 volt DC pumps. I beleive they use less than 10 Amps each.

At 1 level only 1 pump is on, if the level rises above a certain point the second pump also turns on.
And 2 175AH Deep Cycle flooded batteries.

Just my thoughts.

StevenE

 

[SnyperBob]

I was actually thinking about trying something like this myself. Some of those Watch Dog systems are like $500-$750 for everything.

My thoughts were to just run an extension cord from the sump pump to the inverter hooked to my car battery. Leave the car running to recharge the battery. I haven't tried this, but I'm pretty sure just running the pump off the inverter that's connected to just a standalone battery won't last long.

Then again, where I live, we lose power for minutes, not usually hours/days...

Instead of spending less for a DIY solution, you may just want to invest in a quality system. If your basement isn't finished it's probably not a big deal. But if it is finished, you should really consider having a secondary backup pump with backup battery system to supplement your main pump. This will help if you main pump burns up/fails as well.

Some of those Watch Dog batteries will run their systems for a day or two. But those are $100 I think just for the battery (iirc).

 

[drozwood90]

The other issue is, if you switch the relay over too fast, you can damage your pump. You need to de-energize the pump from the wall, THEN bring it in contact with the inverter.

--Dan

 

[politics123]

The other issue is, if you switch the relay over too fast, you can damage your pump. You need to de-energize the pump from the wall, THEN bring it in contact with the inverter.

I think I'll take that risk. Even at peak rain storm, the pump cycles 8 seconds on out of every 80 seconds. Most of time, I cycle 8 seconds on every 5-6 minutes. It would take a particularly well-timed power outtage to hit me in the middle of a pump cycle.

This is some serious amps for a battery and any store battery will not last that long.

True... I'm sizing to automatically support a 8hr period where the pump cycles 6 seconds on every 5 minutes. I figure, given 8hrs without power, I'd be able to take further action.

What 12v pump do you use? I'm not thrilled with the quality of Basement Watchdog. I've been exploring 12v commercial bilge pumps, but its hard to find one that will lift to 8-10' head.

My thoughts were to just run an extension cord from the sump pump to the inverter hooked to my car battery. Leave the car running to recharge the battery. I haven't tried this, but I'm pretty sure just running the pump off the inverter that's connected to just a standalone battery won't last long.

Yup, that's how its connected right now... the install guide says to connect directly off the alternator. At that price, I might just buy a second for that reason.



So back to the relays... any ideas?

 

[Photon]

"What 12v pump do you use? I'm not thrilled with the quality of Basement Watchdog. I've been exploring 12v commercial bilge pumps, but its hard to find one that will lift to 8-10' head."

Do you have a floor drain? Since this arrangement is essentially for emergency use, I'd discharge into the floor drain or laundry tubs so I had only a one foot lift instead of 8-10'. I wouldn't brag about it to the building inspector, though.

I think you would do well to use a 12V pump instead of the inverter as the heat loss through the inverter is significant.

 

[politics123]

"What 12v pump do you use? I'm not thrilled with the quality of Basement Watchdog. I've been exploring 12v commercial bilge pumps, but its hard to find one that will lift to 8-10' head."

Do you have a floor drain? Since this arrangement is essentially for emergency use, I'd discharge into the floor drain or laundry tubs so I had only a one foot lift instead of 8-10'. I wouldn't brag about it to the building inspector, though.

I think you would do well to use a 12V pump instead of the inverter as the heat loss through the inverter is significant.

no floor drain.


The thing I'm must curious about is whether I can connect the inverter to the AC ground. I'd think so... it's just a ground, right?

 

[deranged]

I use 2 Shurflo 1500GPH 12vdc Bilge pumps $60 each. They are rated to lift to 8 ft, I think I am about 7 ft, through the wall to an outside drain that runs under the backyard to a lower section of property.

Correction to the earlier post, they are 2 x 125AH Deep Cycle Batteries from Walmart $79 each.
Some float switches on Ebay $30 and some relays I had laying around.

Since I have solar panels charging the batteries, I changed the 12vDC pumps to primary and setup the 120VAC pump as the backup.
This has been working well for over a year.

The Float switches are also connected to HS and can alert me if the second pump turns on or if the water is higher.
HS also monitors the Battery Voltage.

StevenE

Edit: I have seen the bilge pumps run for over 4 hours continuous on those batteries on a few occassions.

 

[HoustonFirefox]

I agree with Deranged...

Let the exisiting A/C pump do it's thing if you must but I think getting a 12vdc high-capacity pump and running it off of batteries would end up as a good backup (or primary even).

I have bought a 45 watt solar array from Harbor Freight that supplies an amazing amount of power for it's price. I paid $199 locally for it since they were having a sale. Here is the internet link:

http://www.harborfreight.com/cpi/ctaf/disp...temnumber=90599

It will supply up to 3.75 amps of charging current to the battery and the controller that comes with it will cut the supply to the load if the battery voltage falls below 11 volts (to prevent battery damage). In addition it has overcharge protection for the battery (cuts the solar panels out when battery voltage rises above 14.5 volts).

Heck, it even comes with two 5-watt 12 volt florescent lights that would last an eternity on battery power alone! It has an adapter for most small devices and even has a USB port on the front to charge your USB devices!

I've had it up and running now for several weeks and it powers my 12vdc (2500cfm) attic exhaust fans all day long without even getting close to discharging the battery (load is 1.25 amps, but the batteries are being charged at 3.75 amps in full sun).

You could hook your inverter on the battery and run anything you like as well in an emergency.

Be the only guy on your block with power when the storm hits!

Good luck with your project and let us know how it turns out!

 

[hotwire]

Do you have city water, or are you on a well?

 

[politics123]

Do you have city water, or are you on a well?

Yeah, I'm on city water... and I've certainly considered the water-powered sump pump. I'm leaning against it:

1. My house has a pressure regulator (40PSI) even though pressure to the house is 60 PSI. I could easily tap into the 40PSI line, but most of them work best at 60PSI, and that would require a lot of work, since my pressure regulator is in the finished part of the basement.
2. They use a lot of water... We pay $10/thousand gallons for water + sewer, based on the amount of water I use from the meter! The water-power pumps
3. They are only as good as the city pumps. During hurricane isabel, friends of ours lost power and city water for 4 days!
4. They are somewhat expensive to acquire and install. The plumbers do it for $1000. I've never tried plumbing, and while it doesn't look all that complicated, I'm not sure I want to risk it.

 

[politics123]

So today I ran a little test.... connected the inverter to the car battery via jumper cables, plugged in my backup sump pump to the inverter, and power cycled the pump on and off a few times by manipulating the float switch. This turns out to be a pseudo real-world test, since my sump pump cycles on for 8 seconds, clears the pit, and then stays off for a while until the pit is full. [1 minute between cycles during the worst-case scenario, around 5-15 minutes during more typical rainfall]

The car whined a bit, but really nothing too great. Pump ran just fine. The inverter didn't get hot, and the fan didn't turn on.

Next step... still need to find higher capacity (inexpensive) relays, need to acquire a 12v battery (tempted to try a "pre-owned one" to save some bucks), and then a charge-controller

 

[Mccool]

Did you ever do this project? If so, how did it turn out?